Fix bug "kstat binding does not return strings properly"

Fix https://github.com/Nexenta/nef/issues/222

Test:
#  Original output:

~# node  node_modules/kstat/examples/kstat2.js

 [{"class":"device_error","module":"sderr","name":"sd1,err","instance":1,"snaptime":184620382931730,"crtime":362002054477,"data":{"Soft Errors":0,"Hard Errors":0,"Transport Errors":0,"Vendor":86,"Product":86,"Revision":49,"Serial No":54,"Size":32212254720,"Media Error":0,"Device Not Ready":0,"No Device":0,"Recoverable":0,"Illegal Request":0,"Predictive Failure Analysis":0}}]

# Fixed output:

~# node  node_modules/kstat/examples/kstat2.js
 
[{"class":"device_error","module":"sderr","name":"sd1,err","instance":1,"snaptime":184520116487865,"crtime":362002054477,"data":{"Soft Errors":0,"Hard Errors":0,"Transport Errors":0,"Vendor":"VMware, ","Product":"VMware Virtual ","Revision":"1.0 ","Serial No":"6000c29e5c3aac2","Size":32212254720,"Media Error":0,"Device Not Ready":0,"No Device":0,"Recoverable":0,"Illegal Request":0,"Predictive Failure Analysis":0}}]